Visceral fat (including intra-abdominal fat) is fat that surrounds the internal organs, primarily in the abdomen. Visceral fat can include omental fat, which is located on the sheetlike omentum that hangs in front of the intestines within the peritoneal cavity, fat surrounding organs such as the liver, pancreas, spleen, gut, bladder, reproductive organs and kidneys, etc. Visceral fat is qualitatively different from subcutaneous fat, which lies just below the skin and is generally considered to be both less dangerous (with respect to general health) and easier to lose than visceral fat.
Various studies in the literature suggest that an excess of visceral fat can contribute to a variety of health issues, such as heart disease, stroke, type 2 diabetes, etc. Location of such fat can be as important with respect to adverse health effects as the amount of such excess fat. Secondary problems arising from excess body weight stemming from an excess of fat include musculoskeletal problems, arthritis, psychological issues with self-image, and difficulty exercising. The liver also can metabolize visceral fat and release it into the bloodstream as cholesterol. It has been observed that surgical removal of visceral fat in experimental animal models can lead to alleviation of diabetic symptoms, whereas removal of subcutaneous fat has no such discernible effect on health.
Various superficial techniques have been developed for reducing subcutaneous fat, which is generally located just below the skin surface. For example, non-invasive techniques for reducing subcutaneous fat using radiant energy are described in U.S. Pat. Nos. 5,143,063, 5,507,790, and 5,769,879.
Various observations suggest that fat tissue may be sensitive to cold-induced injury. Exposure to low temperatures can cause inflammatory damage and fat necrosis in subcutaneous fat tissue (cold panniculitis). Lipid crystallization in fat cells may be a mechanism by which such disruption of the fatty tissue occurs. For example, infants and young children have been observed to be particularly susceptible to cold panniculitis. This may result from the higher concentration of saturated lipids in fat tissue of children, which tend to have higher melting points. A method and apparatus for reducing subcutaneous fat using contact cooling is disclosed in U.S. Pat. No. 7,367,341. This patent describes disruption of subcutaneous fatty tissue by cooling the fatty tissue below normal body temperature using contact cooling methods and apparatus. A portion of the cooled fatty tissue is gradually resorbed by the body, resulting in a reduction in the amount of subcutaneous fat in the treated area.
However, such techniques for reducing subcutaneous fat are generally not applicable to the deeper visceral fat that is further below the skin surface and is often surrounded by bodily organs. Mechanical removal techniques, such as liposuction, are also not desirable for removing visceral fat because of the significant risks involved with mechanical damage to the organs and tissue structures in the abdomen, such as the peritoneum. There may also be a risk of peritonitis, a serious infection of the abdominal cavity.
Accordingly, visceral fat is harder to remove or reduce than subcutaneous fat in part because it is located deeper within the body. The currently accepted techniques for reducing visceral fat are non-specific approaches, such as diet and exercise.
Techniques have been developed for safely introducing liquids into the peritoneal or abdominal cavity, which is a region of the abdomen located below the lungs and stomach that is lined with a membrane called the peritoneum. For example, a peritoneal dialysis (PD) procedure can be performed to assist the body in removing waste if the kidney function is impaired. A PD procedure includes introduction of a soft tube (e.g., a catheter) into the peritoneal cavity, generally through a small slit formed close to the navel. The abdominal cavity is then filled with a dialysis solution, which is allowed to remain in the body for an extended period of time, referred to as a ‘dwell time,’ that is often between about 4 and 6 hours. During this treatment, the peritoneal membrane allows waste products and extra fluid to pass from the blood into the dialysis solution. The dialysis solution is subsequently drained, which also removes wastes along with the drained fluid. The time needed to fill or drain the dialysis solution is typically about 30 to 40 minutes.
The dialysis solution used in PD procedures is heated to approximately body temperature prior to pumping it into the abdominal cavity. Such heating is required for this procedure to maintain a substantially uniform normal body temperature in the abdomen during the PD procedure.
It would be desirable to selectively and controllably cool the abdominal cavity, and to damage fatty tissue such as adipocytes of the intra-abdominal (visceral) fatty tissue without causing injury to the surrounding tissue and organs. Both health and cosmetic benefits may result from reduction of fatty tissue. However, current methods for subcutaneous fat reduction, such as liposuction, involve invasive procedures with potentially life-threatening risks (e.g., excessive bleeding, mechanical damage to internal organ tissues, etc.). Further, such procedures may not be suitable for physically removing visceral fat, which may be more viscous and rigid than subcutaneous fat.